Goodness knows that Obama's vulnerable to that sort of thing, although fortunately it was apparently too late for Clinton to capitalize on that. Simon of Classical Values (via Glenn) addresses the latest iteration of this vulnerability, which is not happening too late for McCain to capitalize on it. What makes it especially choice is that Simon does it by going through Saul Alinsky's own Rules for Radicals, which is probably racist of him, and by "racist" I mean "effective against Obama."
Personally, if I was running the Obama campaign I'd be looking to break contact this week by any freaking means necessary. It's not just McCain knocking him now: he's getting hit by the State Party organizations.
Or maybe that's "racist," too.